Stylus to host synchronization

ABSTRACT

A system and method for synchronizing a stylus to a capacitive sense array. The system including a capacitive sense array which includes a plurality of electrodes. A synchronization signal is transmitted to the stylus using the plurality of electrodes. The synchronization signal is transmitted to the stylus by capacitively coupling the stylus to the capacitive sense array.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/599,332, filed on Feb. 15, 2012, the contents of which are herebyincorporated by reference herein.

BACKGROUND

1. Technical Field

This disclosure relates to the field of user interface devices and, inparticular, to capacitive sensor devices.

2. Description of the Related Art

The use of a stylus with a touch screen interface is well established.Touchscreen designs have incorporated many different technologiesincluding resistive, capacitive, inductive, and radio frequency sensingarrays. Resistive touch screens, for example, are passive devices wellsuited for use with a passive stylus. The original PalmPilots® devicesfrom the mid-1990s were one of the first successful commercial devicesto utilize a resistive touch screen designed for use with a stylus andhelped to popularize that technology. Although resistive touch screenscan sense the input from nearly any object, multi-touch is generally notsupported. An example of a multi-touch application may be applying twoor more fingers to the touch screen. Another example may be inputting asignature, which may include simultaneous palm and stylus input signals.Due to these and other numerous disadvantages, capacitive touch screensare increasingly replacing resistive touch screens in the consumermarketplace.

Various tethered active stylus approaches have been implemented for usewith touch screens and are found in many consumer applications such aspoint-of-sale terminals (e.g., the signature pad used for credit cardtransactions in retail stores) and other public uses.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is illustrated by way of example, and not oflimitation, in the figures of the accompanying drawings in which:

FIG. 1 is a block diagram illustrating one embodiment of an electronicsystem having a processing device for detecting a presence of a touchobject and a stylus.

FIG. 2 is a block diagram illustrating one embodiment of a systemincluding a capacitive sense array, a stylus, and a processing devicethat converts measured signals to touch coordinates.

FIG. 3 is a block diagram illustrating one embodiment of a stylusconfigured to synchronize to a host.

FIG. 4 is a block diagram illustrating another embodiment of a stylusconfigured to synchronize to a host.

FIG. 5 is a flow chart of one embodiment of a method of synchronizing astylus to a host.

FIG. 6 is a flow chart of another embodiment of a method ofsynchronizing a stylus to a host.

FIG. 7 is a block diagram illustrating a further embodiment of a systemincluding a capacitive sense array, a stylus, and a processing devicethat converts measured signals to touch coordinates.

FIG. 8 is a block diagram illustrating yet another embodiment of astylus configured to synchronize to a host.

FIG. 9 is a timing diagram illustrating an embodiment of asynchronization between a stylus and a host.

FIG. 10 is a timing diagram illustrating another embodiment of asynchronization between a stylus and a host.

FIG. 11 is a flow chart of a further embodiment of a method ofsynchronizing a stylus to a host.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be evident, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-known circuits,structures, and techniques are not shown in detail, but rather in ablock diagram in order to avoid unnecessarily obscuring an understandingof this description. Thus, the specific details set forth are merelyexemplary. Particular implementations may vary from these exemplarydetails and still be contemplated to be within the scope of the presentinvention. Reference in the description to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. The phrase “in oneembodiment” located in various places in this description does notnecessarily refer to the same embodiment.

Apparatuses and methods of synchronizing a stylus to a capacitive sensearray are described. In one embodiment, the capacitive sense array isconfigured to transmit a synchronization signal to the stylus. Aprocessing device provides a synchronization signal to synchronize thecapacitive sense array and the stylus. One or more of the electrodes inthe capacitive sense array may be used to capacitively couple thesynchronization signal to the stylus. The one or more electrodes in thecapacitive sense array may also be used to transmit a host transmit (TX)signal. In one embodiment, the host TX signal and the synchronizationsignal may be transmitted simultaneously (e.g., there is an overlap inthe time period in which the host TX signal is transmitted and the timeperiod in which the synchronization signal is transmitted). In anotherembodiment, the host TX signal and the synchronization signal may havedifferent frequencies (e.g., host TX signal may have higher or lowerfrequency than synchronization signal or vice versa). In one embodiment,the stylus may detect, listen or scan for the host TX signal and maysynchronize its operation to the time intervals (e.g., gaps) between thetransmissions of the host TX signal. The stylus may transmit a stylus TXsignal in the gaps between the transmission of the host TX signal.

FIG. 1 is a block diagram illustrating one embodiment of an electronicsystem 100 having a processing device 110 for detecting a presence of atouch object 140 and a stylus 130. Electronic system 100 includesprocessing device 110, capacitive sense array 125, stylus 130, hostprocessor 150, embedded controller 160, and non-capacitive senseelements 170. In the depicted embodiment, the electronic system 100includes the capacitive sense array 125 coupled to the processing device110 via bus 122. The capacitive sense array 125 may include amulti-dimension capacitive sense array. The multi-dimension sense arrayincludes multiple sense elements, organized as rows and columns. Inanother embodiment, the capacitive sense array 125 operates as anall-points-addressable (“APA”) mutual capacitive sense array. In anotherembodiment, the capacitive sense array 125 operates as a coupled-chargereceiver. Alternatively, other configurations of capacitive sense arraysmay be used. In one embodiment, the capacitive sense array 125 may beincluded in an ITO panel or a touch screen panel.

The operations and configurations of the processing device 110 and thecapacitive sense array 125 for detecting and tracking the touch object140 and stylus 130 are described herein. In short, the processing device110 is configured to detect a presence of the active stylus 130 on thecapacitive sense array 125, as well as a presence of the touch object140. The processing device 110 may detect and track the active stylus130 and the touch object 140 individually on the capacitive sense array125. In one embodiment, the processing device 110 can detect and trackboth the active stylus 130 and touch object 140 concurrently on thecapacitive sense array 125. In one embodiment, the processing device 110is configured to operate as the timing “master,” and the active stylus130 adjusts its timing to match that of the processing device 110 whenthe active stylus 130 is in use. In one embodiment, the capacitive sensearray 125 capacitively couples with the active stylus 130, as opposed toconventional inductive stylus applications. It should also be noted thatthe same assembly used for the capacitive sense array 125, which isconfigured to detect touch objects 140, is also used to detect and trackthe active stylus 130 without an additional PCB layer for inductivelytracking the active stylus 130 as done conventionally.

In the depicted embodiment, the processing device 110 includes analogand/or digital general purpose input/output (“GPIO”) ports 107. GPIOports 107 may be programmable. GPIO ports 107 may be coupled to aProgrammable Interconnect and Logic (“PIL”), which acts as aninterconnect between GPIO ports 107 and a digital block array of theprocessing device 110 (not shown). The digital block array may beconfigured to implement a variety of digital logic circuits (e.g., DACs,digital filters, or digital control systems) using, in one embodiment,configurable user modules (“UMs”). The digital block array may becoupled to a system bus. Processing device 110 may also include memory,such as random access memory (“RAM”) 105 and program flash 104. RAM 105may be static RAM (“SRAM”), and program flash 104 may be a non-volatilestorage, which may be used to store firmware (e.g., control algorithmsexecutable by processing core 102 to implement operations describedherein). Processing device 110 may also include a memory controller unit(“MemCV”) 103 coupled to memory and the processing core 102.

The processing device 110 may also include an analog block array (notshown). The analog block array is also coupled to the system bus. Analogblock array also may be configured to implement a variety of analogcircuits (e.g., ADCs or analog filters) using, in one embodiment,configurable VMs. The analog block array may also be coupled to the GPIO107.

As illustrated, capacitance sensor 101 may be integrated into processingdevice 110. Capacitance sensor 101 may include analog I/O for couplingto an external component, such as capacitive sense array 125,touch-sensor slider (not shown), touch-sensor buttons (not shown),and/or other devices. The capacitance sensor 101 may be configured tomeasure capacitance using mutual capacitance sensing techniques, selfcapacitance sensing technique, charge coupling techniques or the like.In one embodiment, capacitance sensor 101 operates using a chargeaccumulation circuit, a capacitance modulation circuit, or othercapacitance sensing methods known by those skilled in the art. In anembodiment, the capacitance sensor 101 is of the Cypress TMA-3xx familyof touch screen controllers. Alternatively, other capacitance sensorsmay be used. The mutual capacitive sense arrays, or touch screens, asdescribed herein, may include a transparent, conductive sense arraydisposed on, in, or under either a visual display itself (e.g. LCDmonitor), or a transparent substrate in front of the display. In oneembodiment, the transmit (TX) and received (RX) electrodes areconfigured in rows and columns, respectively. It should be noted thatthe rows and columns of electrodes can be configured as TX or RXelectrodes by the capacitance sensor 101 in any chosen combination. Inone embodiment, the TX and RX electrodes of the sense array 125 areconfigured to operate as a TX and RX electrodes of a mutual capacitivesense array in a first mode to detect touch objects, and to operate aselectrodes of a coupled-charge receiver in a second mode to detect astylus on the same electrodes of the sense array. The stylus, whichgenerates a stylus TX signal when activated, is used to couple charge tothe capacitive sense array, instead of measuring a mutual capacitance atan intersection of a RX electrode and a TX electrode (a sense element)as done during mutual capacitance sensing. The capacitance sensor 101does not use mutual capacitance or self-capacitance sensing to measurecapacitances of the sense elements when performing a stylus scan.Rather, the capacitance sensor 101 measures a charge that iscapacitively coupled between the sense array 125 and the stylus 130 asdescribed herein. The capacitance associated with the intersectionbetween a TX electrode and an RX electrode can be sensed by selectingevery available combination of TX electrode and RX electrode. When atouch object, such as a finger or stylus, approaches the capacitivesense array 125, the object causes a decrease in capacitance affectingsome of the electrodes. Thus, the location of the finger on thecapacitive sense array 125 can be determined by identifying both the RXelectrode having a decreased coupling capacitance between the RXelectrode and the TX electrode to which the TX signal was applied at thetime the decreased capacitance was measured on the RX electrode.Therefore, by sequentially determining the capacitances associated withthe intersection of electrodes, the locations of one or more inputs canbe determined. It should be noted that the process can calibrate thesense elements (intersections of RX and TX electrodes) by determiningbaselines for the sense elements. It should also be noted thatinterpolation may be used to detect finger position at betterresolutions than the row/column pitch as would be appreciated by one ofordinary skill in the art having the benefit of this disclosure. Inaddition, various types of algorithms (e.g., approximation algorithms,interpolation algorithms, centroid algorithms) may be used to detect thecenter of the touch as would be appreciated by one of ordinary skill inthe art having the benefit of this disclosure.

In an embodiment, the electronic system 100 may also includenon-capacitive sense elements 170 coupled to the processing device 110via bus 171 and GPIO port 107. The non-capacitive sense elements 170 mayinclude buttons, light emitting diodes (“LEDs”), and other userinterface devices, such as a mouse, a keyboard, or other functional keysthat do not use capacitance sensing. In one embodiment, buses 122, and171 are embodied in a single bus. Alternatively, these buses may beconfigured into any combination of one or more separate buses

Processing device 110 may include internal oscillator/clocks 106 andcommunication block (“COM”) 108. In another embodiment, the processingdevice 110 includes a spread spectrum clock (not shown). Theoscillator/clocks block 106 provides clock signals to one or more of thecomponents of processing device 110. Communication block 108 may be usedto communicate with an external component, such as a host processor 150,via host interface (“I/F”) line 151. Alternatively, processing device110 may also be coupled to embedded controller 160 to communicate withthe external components, such as host processor 150. In one embodiment,the processing device 110 is configured to communicate with the embeddedcontroller 160 or the host processor 150 to send and/or receive data.

Processing device 110 may reside on a common carrier substrate such as,for example, an integrated circuit (“IC”) die substrate, a multi-chipmodule substrate, or the like. Alternatively, the components ofprocessing device 110 may be one or more separate integrated circuitsand/or discrete components. In one exemplary embodiment, processingdevice 110 is the Programmable System on a Chip (PSoC®) processingdevice, developed by Cypress Semiconductor Corporation, San Jose, Calif.Alternatively, processing device 110 may be one or more other processingdevices known by those of ordinary skill in the art, such as amicroprocessor or central processing unit, a controller, special-purposeprocessor, digital signal processor (“DSP”), an application specificintegrated circuit (“ASIC”), a field programmable gate array (“FPGA”),or the like.

It should also be noted that the embodiments described herein are notlimited to having a configuration of a processing device coupled to ahost, but may include a system that measures the capacitance on thesensing device and sends the raw data to a host computer where it isanalyzed by an application. In effect, the processing that is done byprocessing device 110 may also be done in the host.

Capacitance sensor 101 may be integrated into the IC of the processingdevice 110, or alternatively, in a separate IC. Alternatively,descriptions of capacitance sensor 101 may be generated and compiled forincorporation into other integrated circuits. For example, behaviorallevel code describing the capacitance sensor 101, or portions thereof,may be generated using a hardware descriptive language, such as VHDL orVerilog, and stored to a machine-accessible medium (e.g., CD-ROM, harddisk, floppy disk, etc.). Furthermore, the behavioral level code can becompiled into register transfer level (“RTL”) code, a netlist, or even acircuit layout and stored to a machine-accessible medium. The behaviorallevel code, the RTL code, the netlist, and the circuit layout mayrepresent various levels of abstraction to describe capacitance sensor101.

It should be noted that the components of electronic system 100 mayinclude all the components described above. Alternatively, electronicsystem 100 may include some of the components described above.

In one embodiment, the electronic system 100 is used in a tabletcomputer. Alternatively, the electronic device may be used in otherapplications, such as a notebook computer, a mobile handset, a personaldata assistant (“PDA”), a keyboard, a television, a remote control, amonitor, a handheld multi-media device, a handheld media (audio and/orvideo) player, a handheld gaming device, a signature input device forpoint of sale transactions, an eBook reader, a smart phone, a globalposition system (“GPS”) device, or a control panel. The embodimentsdescribed herein are not limited to touch screens or touch-sensor padsfor notebook implementations, but can be used in other capacitivesensing implementations, for example, the sensing device may be atouch-sensor slider (not shown) or touch-sensor buttons (e.g.,capacitance sensing buttons). In one embodiment, these sensing devicesinclude one or more capacitive sensors. The operations described hereinare not limited to notebook pointer operations, but can include otheroperations, such as lighting control (dimmer), volume control, graphicequalizer control, speed control, or other control operations requiringgradual or discrete adjustments. It should also be noted that theseembodiments of capacitive sensing implementations may be used inconjunction with non-capacitive sensing elements, including but notlimited to pick buttons, sliders (ex. display brightness and contrast),scroll-wheels, multi-media control (ex. volume, track advance, etc.)handwriting recognition, and numeric keypad operation.

FIG. 2 is a block diagram illustrating one embodiment of a system 200including a capacitive sense array 201, a stylus 130, and a processingdevice 110 that converts measured signals to touch coordinates. Theprocessing device 110 includes a processing core 210, a TX drivercircuit 212, a RX sense circuit 214, a multiplexer 218, and a modulator219. In one embodiment, the processing core 210 is similar to thecapacitance sensor 101 described above. The sense array 201 includesmultiple electrodes that can be configured as TX electrodes or RXelectrodes. For example, in one mode, the TX drive circuit 212 drives aTX signal on a first set of TX electrodes (e.g., the horizontalelectrodes), and the RX sense circuit 214 measures signals on a secondset of RX electrodes (e.g., the vertical electrodes). In another mode,the TX electrodes are RX electrodes and the RX sense circuit 214 isconfigured to measure signals on two sets of RX electrodes (e.g., onboth the vertical and horizontal electrodes). These sets of RXelectrodes can be considered as separate receive channels for stylussignal sensing. It should be noted that TX and RX electrodes are alsoreferred to as TX and RX lines. The multiplexer 218 can be used toconnect the TX electrodes or the RX electrodes to the TX drive circuit212 or the RX sense circuit 214 based on whether the electrodes arebeing used as RX electrodes or TX electrodes. Although the multiplexer218 is shown as part of the processing device 110, in other embodiments,the processing device 110 may not include the multiplexer 218. In oneembodiment, the system 200 may include multiple sensor arrays. Thesystem may also include individual TX driver circuits and RX sensecircuits for each of the multiple sense arrays.

In one embodiment, during normal finger scanning, a passive object(e.g., a finger or other conductive object) touches the sense array 201at contact point (not illustrated in FIG. 2). The TX drive circuit 212drives the TX electrodes with a TX signal. The RX sense circuit 214measures the RX signals on RX electrodes. In an embodiment, theprocessing core 210 determines the location of contact point based onthe mapping techniques as would be appreciated by one of ordinary skillin the art having the benefit of this disclosure. Alternatively, othertechniques may be used to determine the contact point. The TX electrodesand RX electrodes are multiplexed by multiplexor 218. The processingcore 210 provides the TX signal on the TX electrodes (rows) and measuresthe capacitance coupling on the RX electrodes (columns). In anembodiment, the TX and RX electrodes are orthogonal and may be usedinterchangeably (e.g., transmitting on columns and receiving on rows).In an embodiment, the TX drive circuit 212 transmits the TX signalthrough a high impedance ITO panel (TX electrodes), thus limiting theupper frequency limit and speed of the system. The total scan time mayalso dependent upon the number of TX electrodes and RX electrodes in thesense array 201. For example, the TX drive circuit 212 provides a TXsignal on a single TX electrode and simultaneously reads thecapacitively coupled RX signal on a RX electrode, according to oneembodiment. In another embodiment, the RX electrodes 640 are multiplexedin two or more scans. In another embodiment, the TX signal may beapplied to more than one electrode at the same time.

In one embodiment, during stylus scanning, the stylus TX drive circuit222 of stylus 130 provides a TX signal 227 directly to contact point 228on sense array 201, thus eliminating the need to dedicate the second setof RX electrodes (previously TX in finger scanning) to transmitting a TXsignal from the TX drive circuit 212. In one embodiment, the activestylus 130 may not directly contact the electrodes in the sense array201. The active stylus 130 may contact a substrate above the sense array201 or may contact a substrate on which the sensor array 201 isdeposited. The substrate may be a dielectric material. As such, the RXsense circuit 214 measures the RX signal on both the first set of RXelectrodes (rows) and a second set of RX electrodes (columns) of sensearray 201. This may result in faster position tracking because the TXsignal no longer passes through two high impedance ITO electrodes (e.g.,passes from a TX electrode to an RX electrode) but instead passesthrough one high impedance ITO electrode, thus reducing the scan time tothe total RX measurement. In one embodiment, during touch objectdetection (e.g., when detecting a touch object such as a finger), the TXsignal passes through a first high impedance ITO electrode (e.g., a TXelectrode) and then passes through a second high impedance ITO electrode(e.g., an RX electrode).

The active stylus 130 includes the TX drive circuit 222, amicrocontroller (MeU) 224, and a receiver 226. In one embodiment, theprocessing core 210 performs a normal scan of the sense array 201 duringRX sensing of TX signal from the TX drive circuit 212 (described above),and a stylus scan of the sense array 201 during RX sensing of the stylusTX signal 227 (illustrated in FIG. 2). For the stylus scan, theprocessing core 210 measures a charge being capacitively coupled to therow and column electrodes of the sense array from the stylus. To furtherillustrate, a mutual capacitance scan uses both a TX and RX signal totrack an object. As described above, this is typically done by scanningthe RX electrodes for the driven TX electrode in a successive fashion bythe processing core 210. In an array of N rows (TX signal) and M columns(RX signal), a complete scan would perform N×M total scans if one RXelectrode is sensed at a time. For example, transmitting a TX signal(“TX′ing”) on row 1, and receiving a receive signal (“RX′ing”) oncolumns 1-M, followed by TX′ing on row 2 and RX′ing on columns 1-M, andso on in sequential fashion. Alternatively, more RX electrodes can besensed at a time. In one embodiment, 4 or 8 RX electrodes are sensed ata time, but in other embodiments, all RX electrodes may be sensedsimultaneously or sequentially. With multiple RX channels to sense morethan one RX electrode at the same time, the complete scan would be(N*M)/(# RX channels). In contrast, a stylus scan may not use a TXsignal by the TX drive circuit 212 and a complete scan would perform asingle RX signal measurement on each row and column, or N+M scans, thusresulting in a significantly reduced stylus scanning time for the entiresense array as compared with mutual capacitance scanning time for theentire sense array. Like above, multiple RX channels can be used tosense multiple RX electrodes at the same time. In this case, thecomplete scan would be (N+M)/(# RX channels).

In one embodiment, the operation of the stylus 130 is synchronized withthe operation of the sense array 201. For example, the stylus 130 maynot transmit a TX signal when the sense array 201 is performing touchobject detection (e.g., transmitting a TX signal on a first set ofelectrodes and receiving the TX signal on a second set of electrodes).In another example, the sense array 201 may not perform touch objectdetection and may “listen” or “scan” on all of the electrodes for a TXsignal from the stylus 130 when the stylus 130 transmits the TX signal.Synchronizing the operation of the stylus and the sense array 201 mayreduce the amount of interference when the sense array 201 detects theTX signal from the stylus 130 and may also reduce the power consumptionof the stylus 130 because the stylus 130 may transmit the TX signal at alower power. Synchronizing the operation of the stylus 130 and the sensearray 201 may also provide more flexibility in the management of thestylus and touch object scanning (e.g., allow for different reportingrates for stylus and touch objects under different conditions).

In the depicted embodiment, the TX driver circuit 222 generates a stylusTX signal 227 from the tip of the active stylus 130 into the touchscreen. In one embodiment, the MCV may be implemented using acombination of processing logic, state machines, and other circuitry.The processing core 210 senses this signal and resolves this to be thepoint of the active stylus 130. Synchronization between the processingcore 210 sensing and the TX signal 227 generated by the active stylus130 is used to obtain correct operation. In one embodiment, thissynchronization may be performed using one or more of the electrodes ofthe sense array 201 to transmit a synchronization signal 230 to theactive stylus 130. The active stylus 130 may detect (e.g., sense) anddemodulate the synchronization signal 230 using receiver 226. The MCV224 may process the synchronization signal 230 to synchronize the timingof the sensing performed by the processing core 210 and the transmissionof the TX signal 227 by the active stylus 130. In one embodiment, themodulator 219 may be used to generate the synchronization signal 230which is transmitted by the one or more electrodes of the sense array201.

In one embodiment, the synchronization signal 230 may be transmittedfrom the one or more electrodes of the sense array 201 to the activestylus 130 by capacitively coupling the one or more electrodes of thesense array 201 to the active stylus 130. In another embodiment, thesynchronization signal 230 may have a higher frequency than the TXsignal which is also transmitted by the one or more electrodes of thesense array 210. In a further embodiment, the synchronization signal 230may be a high frequency signal (e.g., a 13.56 megahertz (MHz) on-offkeying (OOK) or amplitude shift-keying (ASK) signal). In one embodiment,the frequency range of the synchronization signal 230 may be from 400KHz to 15 MHz, based on the RC constant of the ITO panel. In oneembodiment, the frequency of the synchronization signal 230 may be afrequency which is easily detected by low-cost or low-power circuits. Inone embodiment, the frequency of the synchronization signal 230 may be amultiple of the frequency of the TX signal which is also transmitted bythe one or more electrodes of the sense array 210. In anotherembodiment, the frequency of the TX signal transmitted by the one ormore electrodes of the sense array 210 may be a multiple of thefrequency of the synchronization signal 230. This may reduce theinterference experienced by the active stylus 230 when the active stylus230 receives the TX signal and the synchronization signal 230transmitted by the one or more electrodes of the sense array 210 (e.g.,may improve or increase the signal to noise ration (SNR) of the TXsignal and the synchronization signal 230).

In some embodiments, synchronization signal 230 may be transmitted bythe one or more electrodes of the sense array 210 in a variety ofmethods. For example, every other vertical electrode or every otherhorizontal electrode in the sense array 210 may transmit thesynchronization signal 230. In another example, the vertical electrodesmay transmit the synchronization signal 230 for a period of time,followed by the horizontal electrodes. In a further example, thesynchronization signal may transmitted by the sequentially using theelectrodes of the sense array (e.g., the first vertical electrode maytransmit the synchronization signal, followed by the second verticalelectrode, followed by the third vertical electrode, etc.).

In one embodiment, the operation of the stylus and the host may besynchronized on a cycle by cycle basis. For example, the rising andfalling edges of the TX signals transmitted by the host and the stylusmay be synchronized (e.g., may be in phase). In another embodiment, theoperation of the stylus and the host may be synchronized based on burstsor gaps in the TX signals transmitted by the host and the stylus. Forexample, the stylus may transmit the stylus TX signal only in the gaps(e.g., time intervals) between the host TX signals.

As described above, a passive stylus may be used as a touch object tointerface with the various touch screens described above. In contrast topassive styluses, an active stylus 130 provides the transmit signal 227(TX signal). This signal 227 may be provided to the active stylus 130 bythe processing core 210 as part of the synchronization. The activestylus 130 capacitively couples the stylus TX signal 227 to the sensearray 201. In an embodiment, the stylus signal amplitude, frequency,phase, etc., may be the same or similar to that which is utilized forfinger sensing by the processing core 210. Alternatively, the stylus TXsignal may be different than the TX signal from the TX drive circuit212, in one or more of amplitude, frequency, and phase. In anotherembodiment, the stylus TX signal may have a different code for codemodulation than a code used in the TX signal from the TX drive circuit212. In an exemplary embodiment, the stylus TX signal 227 has greateramplitude than the finger sensing TX signal from the TX drive circuit212. For example, in one exemplary embodiment, the stylus TX signal 227ranges from approximately 20-50V, as compared with the approximately5-10V typically provided by the processing core 210. Alternatively,other voltages may be used as would be appreciated by one of ordinaryskill in the art. The higher stylus TX voltage couples more charge tothe sense array 201 more quickly, thus reducing the amount of time usedto sense each row and column of the sense array 201. Other embodimentsmay incorporate higher voltages on the sense array TX electrodes toobtain similar time efficiency improvements for finger sensing.

In an embodiment, the active stylus 130 applies a higher frequency onthe stylus TX signal 227 than the TX signal frequency from TX drivecircuit 212 to achieve a reduced sensing time. Charge may becapacitively coupled from the active stylus 130 to the sense array 201during the rising and falling edges of the stylus TX signal 227. Thus, ahigher TX frequency provides a greater number of rising and fallingedges over a given period of time, resulting in greater charge coupling.The practical upper limit of the TX frequency in finger sensing mode(e.g., TX signal on sense array 201 for finger sensing) is dependentupon the resistor-capacitor (“RC”) time constant of the panel'sindividual sense elements and interconnect (not shown). This istypically due to high impedance materials (e.g. ITO) used in thefabrication of the sense array 201. A high-impedance sense array (e.g.,sense array 201) may result in a high time constant and resulting signalattenuation of the rows (TX electrodes) and columns (RX electrodes) ofsense elements, which may limit the maximum sensing frequency. Whenusing an active stylus to transmit the stylus TX signal 227 directly toa contact point 228 on sense array 201, the stylus TX signal 227 doesnot pass through part of the high impedance path, and therefore themaximum operating frequency for the stylus TX signal 227 can beincreased. For example, the time constant of the RX traces (both rowsand columns) may be used to determine an upper frequency limit, but thiswill typically be is at least double the upper frequency limit used infinger sensing. Typically the impedance is half to the impedance whenperforming mutual capacitance scanning, since the row's impedance iseliminated and the column's impedance remains (or vice versa). In oneembodiment, the frequencies used for finger sensing and stylus sensingmay be similar, and the upper range for the frequencies may bedetermined by one or more of the panel RC time constant, drivingwaveforms, requirements for the panel's resistance to signalinterference, and receiver implementation details.

Although the electrodes (e.g., lines) appear as lines in FIG. 2, theseelectrodes may represent bars or elongated rectangles or othertessellated shapes such as diamonds, rhomboids, and chevrons.Alternatively, other useable shapes may be used as would be appreciatedby one of ordinary skill in the art having the benefit of thisdisclosure

FIG. 3 is a block diagram illustrating one embodiment of a stylus 350configured to synchronize to a host 305.

The host 305 includes an oscillator (OSC) 310, a clock divider 315, anamplitude shift-keying modulator (ASK Mod) 320, a receiver 325, anamplifier 330, a matching circuit 335, and an ITO panel 340. In oneembodiment, the OSC 310 may be used to generate a signal with a givenfrequency, which may be fed to the clock divider 315 to generate a clocksignal. The clock signal generated by the OSC 310 and the clock divider315 may be used to determining the timing of a synchronization signaltransmitted by the ITO panel 340 to the stylus 350.

In one embodiment, the ASK Mod 320 may use the clock signal generated bythe clock divider 315 to perform an ASK modulation on the signalgenerated by the OSC 310, in order to generate the synchronizationsignal which is transmitted by the ITO panel 340 to the stylus 350.Although amplitude shift-keying (“ASK”) is described herein, other typesof modulation schemes may be used (e.g., frequency shift keying (“FSK”),phase-shift keying (“PSK”), binary phase shift keying (“BPSK”)) andwould be known by one of ordinary skill in the art. The synchronizationsignal is provided to the amplifier 330 which amplifies thesynchronization signal. The amplified synchronization signal is providedto the matching circuit 335 which provides impedance matching andcouples synchronization signal from the from the amplifier 330 to theITO panel 340 (to the electrodes of the ITO panel 340).

In one embodiment, the ITO panel 340 may also transmit a host TX signalto the stylus 350. In one embodiment, the synchronization signalgenerated by the OSC 310 and the clock divider 315 may have a higherfrequency (e.g., 13.56 MHz) than the host TX signal transmitted by theITO panel to the stylus 350. In one embodiment, the frequency range ofthe TX signal may be from 400 KHz to 15 MHz, based on the RC constant ofthe ITO panel. In one embodiment, the frequency of the TX signal may bea frequency which is easily detected by low-cost or low-power circuits.

In another embodiment, the ITO panel 340 (e.g., the electrodes of theITO panel 340) may receive a TX signal transmitted by the stylus 350.The TX signal received from the stylus 350 is provided to the matchingcircuit which provides impedance matching and couples the TX signalreceived from the stylus 350 to the receiver 325. In one embodiment, thereceiver 325 may use the synchronization signal generated by the OSC 310and the clock divider 315, to determine when the ITO panel 340 should bescanned (e.g., when the electrodes of the ITO panel should be scanned)in order to detect the TX signal from the stylus 350. For example, basedon the timing of the synchronization signal (which is transmitted to thestylus 350 via the ITO panel 340), the stylus 350 may only transmit theTX signal during certain time intervals, and the receiver 325 may scanthe ITO panel 340 during the same time intervals. In one embodiment, thereceiver 325 may provide the TX signal received from the stylus 350 to aprocessing device (e.g., processing device 110 of FIG. 1) for furtherprocessing.

The stylus 350 includes a stylus tip 351, a matching circuit 355, afilter 360, an amplifier/automatic gain control (AGC) circuit 365, anamplitude (AM) demodulator 370, and a transmit (TX) driver 375.

In one embodiment, the stylus tip 351 may receive the synchronizationsignal transmitted by the ITO panel 340 (e.g., by one or more electrodesof the ITO panel 340). The synchronization signal is provided to thematching circuit 355 which provides impedance matching and couples thesynchronization signal to the filter 360. The filter 360 may be used tofilter the synchronization signal out from other signals which may bereceived (e.g., from a TX signal transmitted by one or more electrodesof the ITO panel 340). The synchronization signal is provided to theamplifier/AGC circuit 365 which amplifies the synchronization signalprovides an automatic gain control loop to maintain a constantsynchronization signal amplitude over a wide-input-signal voltage range.The amplified synchronization signal is provided to the AM demodulator730 which demodulates the synchronization signal to determine when thestylus 350 should transmit a TX signal. The TX driver 375 may transmitthe TX signal to the stylus tip 351 based on the synchronization signal.

FIG. 4 is a block diagram illustrating another embodiment of a stylus450 configured to synchronize to a host 405.

The host 405 includes a clock 410, a frequency converter 415, a receiver420, a matching circuit 425 and an ITO panel 430. The clock 410 may beused to generate a reference signal which may be used to generate asynchronization signal and a host TX signal. The reference signalgenerated by the clock 410 may be provided to the matching circuit 425which provides impedance matching for the reference signal and couplesthe reference signal to the ITO panel 430 as the host TX signal. In oneembodiment, the reference signal generated by the clock 410 may also beused to generate a synchronization signal by increasing (e.g.,multiplying) or decreasing (e.g., dividing) the frequency of thereference signal to generate the synchronization signal. The referencesignal is provided to the frequency converter 415 which increases ordecreases the frequency of the reference signal to generate thesynchronization signal. In one embodiment, the frequency converter 415increases or decreases the frequency of the reference signal and alsomaintains the phase relation between the reference signal and thesynchronization signal. The synchronization signal is provided to thereceiver 420, which uses the synchronization signal to determine when toscan the ITO panel 430 for a TX signal from the stylus 450. In oneembodiment, the matching circuit 425 may also mix the synchronizationsignal and the host TX signal when the two signals are transmitted tothe stylus 450. In another embodiment, the receiver 420 may be a narrowband receiver that is capable of differentiating between (e.g.,separating) the reference signal and a TX signal received from thestylus 450.

In one embodiment, the frequency of the host TX signal may be a multipleof the frequency of the synchronization signal. In another embodiment,the frequency of the synchronization signal may be a multiple of thehost TX signal. Because the frequency of the host TX signal is amultiple of the synchronization signal, or vice versa, the interferencein the signals (e.g., the synchronization signal or the host TX signal)received by the stylus 450 is reduced. This may increase the SNR of thesignals received by the stylus 450 and may increase the ability of thestylus 450 to receive the signals transmitted by the ITO panel 430.

The stylus 450 includes a stylus tip 451, a filter 455, an amplifier/AGCcircuit 460, a frequency converter 465, and a TX driver 470. The stylustip 451 may receive the signals (e.g., a host TX signal and asynchronization signal) from the ITO panel 430. The signals are passedto a filter where the synchronization signal is filtered out from othersignals received form the ITO panel 430. The synchronization signal isprovided to the amplifier/AGC circuit 460 which amplifies thesynchronization signal provides an automatic gain control loop tomaintain a constant synchronization signal amplitude over awide-input-signal voltage range. The amplified synchronization signal isprovided to the frequency converter 465 which increases or decreases thefrequency of the synchronization signal to obtain a TX signal. In oneembodiment, the frequency converters 415 and 465 may operate in anidentical manner (e.g., both frequency shifters 415 and 465 increase ordecrease the frequency of a signal by the same amount). The TX signal isprovided to the TX driver 470 which provides the TX signal to the stylustip 451.

FIG. 5 is a flow chart of one embodiment of a method 500 ofsynchronizing a stylus to a host. The method 500 may be performed by ahost that comprises hardware (e.g., circuitry, electrodes, switches,dedicated logic, programmable logic, microcode), software (e.g.,instructions run on a processing device to perform hardware simulation),or a combination thereof. In one embodiment, method 500 may be performedby processing device 110 as shown in FIG. 1.

The method 500 begins with the host device providing a plurality ofelectrodes in a capacitive sense array (block 505). In one embodiment,the plurality of electrodes may be part of an ITO panel or a touchscreen. At block 510, a synchronization signal is transmitted to astylus using the plurality of electrodes. Any combination or sequence ofthe plurality of electrodes may be used to transmit the synchronizationsignal, as discussed above in conjunction with FIG. 2. In oneembodiment, the frequency of the synchronization signal may be differentfrom the frequency of a host TX signal, which may also be transmittedusing the plurality of electrodes. In another embodiment, the frequencyof the synchronization signal may be higher than the frequency of thehost TX signal. In a further embodiment, the frequency of thesynchronization signal may be lower than the frequency of the host TXsignal.

FIG. 6 is a flow chart of another embodiment of a method ofsynchronizing a stylus to a host. The method 600 may be performed by ahost that comprises hardware (e.g., circuitry, electrodes, switches,dedicated logic, programmable logic, microcode), software (e.g.,instructions run on a processing device to perform hardware simulation),or a combination thereof. In one embodiment, method 600 may be performedby processing device 110 as shown in FIG. 1.

The method 600 begins with the host device providing a plurality ofelectrodes in a capacitive sense array (block 605). In one embodiment,the plurality of electrodes may be part of an ITO panel or a touchscreen. At block 610, the frequency of the synchronization signal isconverted (e.g., increased, decreased, multiplied and/or divided) togenerate a TX signal. In one embodiment, the frequency of thesynchronization signal is a multiple of the frequency of TX signal. Inanother embodiment, the frequency of TX signal is a multiple of thefrequency of the synchronization signal. The synchronization signal istransmitted to a stylus using the plurality of electrodes at block 615.Any combination or sequence of the plurality of electrodes may be usedto transmit the synchronization signal, as discussed above inconjunction with FIG. 2. At block 620, a TX signal is transmitted usingthe plurality of electrodes.

FIG. 7 is a block diagram illustrating a further embodiment of a system700 including a capacitive sense array 701, a stylus 730, and aprocessing device 702 that converts measured signals to touchcoordinates. The processing device 702 includes a processing core 710, aTX driver circuit 712 a RX sense circuit 714, and a multiplexer 718. Inone embodiment, the TX driver circuit 712, the RX sense circuit 714 andthe multiplexer 718 may perform functions similar to the TX drivercircuit 212, the RX sense circuit 214 and the multiplexer 218 of theprocessing device 110 in FIG. 2.

The processing core 710 may also perform functions similar to theprocessing core 210 of the processing device 110 in FIG. 2. In oneembodiment, the processing core 710 may control the timing of a host TXsignal which is transmitted using electrodes (e.g., electrodes) incapacitive sense array 701. The processing core 710 may cause one ormore electrodes of the capacitive sense array 701 to transmit (e.g., theprocessing core 710 may generate) a host TX signal at certain timeintervals (e.g., may transmit a synchronization burst 729). In oneembodiment, the frequency of the synchronization burst 729 may beidentical to the frequency of the host TX signal to one or moreelectrodes in the capacitive sense array 701 may normally transmit. Inanother embodiment, the frequency of the synchronization burst 729 maybe different from the frequency of the host TX signal to one or moreelectrodes in the capacitive sense array 701 may normally transmit. Inone embodiment, the synchronization burst 729 may also carry or includeother data (which may be transmitted to the stylus 730 via thesynchronization burst 729) including but not limited to configurationdata, power management commands, user feed back commands (e.g., acommand to blink a light emitting diode (LED)), data packets, or otheradditional functionality encoded by the host onto the synchronizationburst 729.

The stylus 730 includes a receiver 726, an MeV 724, and a TX drivercircuit 722. The receiver 726 may detect the synchronization burst 729and may provide the synchronization burst 729 to the MeV 724. The MeV724 may process the synchronization burst 729 to synchronize theoperation of the stylus with the host 705. In one embodiment, thesynchronization burst 729 may be a synchronization signal. Based on thesynchronization burst 729, the MeV 724 may generate a TX signal andprovide the TX signal to the TX drive circuit 722 after thesynchronization burst 729 ends (as shown in FIG. 7). The TX drivecircuit 722 may provide the TX signal to the tip of the stylus whichprovides a TX signal 727 directly to contact point 728 on sense array701 (e.g., by capacitively coupling the host 705 and the stylus 730). Inone embodiment, the synchronization burst 729 may be used to determineone or more of the timing of the TX signal 227, the frequency of the TXsignal 727, the phase of the TX signal 727. In one embodiment, suchinformation may be encoded into the synchronization burst 729 such thatthe stylus 730 transmits a TX signal 727 of substantially the same phaseand frequency as that of the synchronization burst 729, at a time fromeither the start or the end of the synchronization burst 729. In anotherembodiment, the any combination of the frequency, timing, and phase ofthe TX signal 727 may be calculated from data encoded in thesynchronization burst 729.

FIG. 8 is a block diagram 800 illustrating yet another embodiment of astylus 850 configured to synchronize to a host 805. The host 805includes an ITO panel 810 and a receiver 815. In one embodiment, the ITOpanel 810 may transmit a synchronization burst using one or moreelectrodes (e.g., electrodes) of the ITO panel 810. As discussed above,the synchronization burst may include other data. The ITO panel 810 mayalso receive a TX signal from the stylus 850 (via capacitive couplingwith the stylus 850) and may provide this TX signal to the receiver 815.The receiver 815 may filter, amplify, or otherwise process the TX signaland may provide the processed TX signal to a processing device in orderto determine a location of contact point between the stylus 850 and theITO panel 810.

The stylus 850 includes a stylus tip 851, a TX filter 855, anamplifier/AGC circuit 860, a TX clock qualifier 865, a phase-locked loop(PLL) circuit 870, a carrier detector 875, and a TX driver 880. In oneembodiment, the functions of some of the circuits shown in FIG. 8 may beperformed by an MCV, rather than a dedicated circuit or component. Thestylus tip 851 may receive signals (including a synchronization burst)transmitted by one or more electrodes of the ITO panel 810. Thesynchronization burst may be provided to the TX filter 855 which mayinitially filter the signal received by the stylus 850. The filteredsignal is provided to the amplifier/AC circuit 860 which amplifies thefiltered signal and provides an automatic gain control loop to maintaina constant synchronization signal amplitude over a wide-input-signalvoltage range. The amplified signal is provided to the carrier detector875 which may process the signal to determine if the amplified signalincludes additional data (e.g., force data, button data, etc.). Theadditional data may be provided to the TX driver 880 which may use theadditional data when providing the stylus TX signal to the stylus tip851.

The amplified signal is also provided to the TX clock qualifier 865. TheTX clock qualifier 865 will filter out the synchronization burst fromthe amplified signal and provides the synchronization burst to the PLLcircuit 870. The PLL circuit 870 may be used to synchronize theoperation of the stylus 850 to the timing of the synchronization burst.As discussed above, the PLL circuit 870 may synchronize the operation ofthe stylus 850 to the host 805 on a cycle by cycle basis. The PLL 870generates a stylus TX signal (which is synchronized to thesynchronization burst) to the TX driver 880 which provides (e.g.,drives) the stylus TX signal to the stylus tip 851. In one embodiment,the PLL 870 may be a digital PLL implemented at least partially infirmware on an MCV.

FIG. 9 is a timing diagram 900 illustrating an embodiment of asynchronization between a stylus and a host. The timing diagram 900includes a host TX signal and a stylus TX signal. As shown in FIG. 9,the host TX signal is transmitted during time intervals 905, 915, 925,and 935 (e.g., the host TX signal is transmitted in bursts). The gapsbetween the time intervals 905, 915, 925, and 935 are shown as timeintervals 910, 920, 930, and 940. The stylus TX signal is transmittedduring the time intervals 910, 920, 930, and 940 (e.g., in between thegaps of the host TX signal).

As discussed above, a processing device may be used to detect thepresence of a touch object and a stylus on a capacitive sense array(e.g., on an ITO panel). When detecting the presence of a touch object(e.g., of a finger), the capacitive sense array may transmit the host TXsignal on one set of electrodes (e.g., vertical electrodes) and mayreceive the host TX signal on a different set of electrodes (e.g.,horizontal electrodes). When detecting a stylus, the capacitive sensearray may use all of the electrodes in the capacitive sense array as RXsensors to detect the stylus TX signal. Synchronizing the transmissionsof the host TX signal (used to detect a touch object) and the stylus TXsignal (used to detect the stylus) allows both touch object and thestylus to be used simultaneously on the capacitive sense array.

In one embodiment, the stylus may listen or detect the host TX signal todetermine the time intervals 905, 915, 925, and 935 of the host TXsignal. After determining the time intervals 905, 915, 925, and 935 ofthe host TX signal, the stylus may synchronize its operation to the timeintervals 905, 915, 925, and 935 of the host TX signal, such that thestylus transmits the stylus TX signal only within the gaps between timeintervals 905, 915, 925, and 935 of the host TX signal (e.g., onlywithin time intervals 910, 920, 930, and 940). In one embodiment, thestylus transmits a stylus TX signal matching the phase and/or frequencyof the host TX signal for a pre-determined time after the end of thehost TX signal burst is detected.

FIG. 10 is a timing diagram 1000 illustrating another embodiment of asynchronization between a stylus and a host. The timing diagram 100includes a host TX timeline, a stylus TX timeline, and a host RX timeline.

As shown in FIG. 10, the host transmits a synchronization burst at timeinterval 1005. The stylus may detect the synchronization bursttransmitted at time interval 1005 and synchronize the operation of thestylus to the host using the synchronization burst (e.g., using the PLLdescribed above to synchronize with the synchronization burst). Thestylus may also transmit a stylus TX signal after the synchronizationburst ends at time interval 1020. The host may listen (e.g., detect) thestylus TX signal at time interval 1010, to confirm that a stylus ispresent on the capacitive sense array. After confirming that the stylusis present on the capacitive sense array, the host will listen (e.g.,detect) on one or more of the rows and columns of electrodes in thecapacitive sense array for the stylus TX signal at time interval 1015.

In one embodiment, the host may transmit a host TX signal on a first setof electrodes at time interval 1025 and may receive or detect the hostTX signal on a second set of electrodes at time interval 1030 (e.g., mayperform touch object detection). At time interval 1035, the host TXtimeline, a stylus TX timeline, and a host RX timeline may restart suchthe host again transmits a synchronization burst at time interval 1035and the host again listens (e.g., scans the RX electrodes) for a stylusTX signal at time interval 1040.

FIG. 11 is a flow chart of a further embodiment of a method 1100 ofsynchronizing a stylus to a host. The method 1100 may be performed by ahost that comprises hardware (e.g., circuitry, electrodes, switches,dedicated logic, programmable logic, microcode), software (e.g.,instructions run on a processing device to perform hardware simulation),or a combination thereof. In one embodiment, method 1100 may beperformed by processing device 702 as shown in FIG. 7.

The method 1100 begins with the host device providing a plurality ofelectrodes in a capacitive sense array (block 1105). In one embodiment,the plurality of electrodes may be part of an ITO panel or a touchscreen. At block 1110, a synchronization burst is transmitted to astylus at a first time interval, using the plurality of electrodes. Anycombination or sequence of the plurality of electrodes may be used totransmit the synchronization signal, as discussed above in conjunctionwith FIG. 2. In one embodiment, the frequency of the synchronizationburst may the same as the frequency of a TX signal which may betransmitted by the host device. The host device listens (e.g., scans ordetects) for a stylus TX signal at a second time interval using theplurality of electrodes at block 1115 (e.g., touch object detection). Atblock 1120, the host device transmits a host TX signal using the rows ofelectrodes and detects the host TX signal using the columns ofelectrodes at a third time interval. In one embodiment, the host devicemay transmit the host TX signal using the columns of electrodes and maydetect the host TX signal using the rows of electrodes.

The embodiments described herein describe various aspects of stylus tohost synchronization methods. In one embodiment, a synchronizationsignal may be transmitted to a stylus using one or more electrodes in acapacitive sense array. The one or more electrodes are also used totransmit a host TX signal. In another embodiment, the one or moreelectrodes may transmit a synchronization burst (e.g., transmit a signalfor a period of time) and the stylus may synchronize its operation tothe host by listening or detecting the synchronization burst. Some ofthe embodiments described herein allow a stylus to synchronize itsoperation to the host without using an antennae (e.g., without using aradio frequency (RF) antennae or a magnetic antennae).

In one embodiment, the synchronization signal is capacitively coupled toa stylus from the sense array of a host device, rather than transmittedusing a wireless signal, such as an RF signal. In another embodiment,the host device may be classified as an unintentional radiator (e.g., adevice which does not intentionally transmit RF). Because the hostdevice may be classified as an unintentional radio, the host device maybe subject to fewer certification requirements (as compared to deviceswhich intentionally radiate or transmit RF) which may decrease thedevelopment costs and development times of the host device.

Embodiments of the present invention, described herein, include variousoperations. These operations may be performed by hardware components,software, firmware, or a combination thereof. Any of the signalsprovided over various buses described herein may be time multiplexedwith other signals and provided over one or more common buses.Additionally, the interconnection between circuit components or blocksmay be shown as buses or as single signal lines. Each of the buses mayalternatively be one or more single signal lines and each of the singlesignal lines may alternatively be buses.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a computer-readable medium.These instructions may be used to program a general-purpose orspecial-purpose processor to perform the described operations. Acomputer-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a machine (e.g., a computer). Thecomputer-readable storage medium may include, but is not limited to,magnetic storage medium (e.g., floppy diskette); optical storage medium(e.g., CD-ROM); magneto-optical storage medium; read-only memory (ROM);random-access memory (RAM); erasable programmable memory (e.g., EPROMand EEPROM); flash memory, or another type of medium suitable forstoring electronic instructions. The computer-readable transmissionmedium includes, but is not limited to, electrical, optical, acoustical,or other types of mediums.

Additionally, some embodiments may be practiced in distributed computingenvironments where the computer-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the transmission medium connecting the computer systems.

Although the operations of the methods) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

1. An active stylus configured to provide input to a sensor arrayincluding first electrodes extending in a first direction and secondelectrodes extending in a second direction different from the firstdirection, the active stylus comprising: signal reception circuitryconfigured to receive first signal from the sensor array based oncapacitive coupling between the active stylus and the sensor array;signal transmission circuitry configured to transmit, in response to thefirst signal, second signal to the sensor array based on capacitivecoupling between the active stylus and the sensor array; and controlcircuitry configured to control operation of the signal receptioncircuitry and the signal transmission circuitry to synchronizetransmission timing of the second signal to the sensor array withreception timing of the first signal from the sensor array.
 2. Theactive stylus of claim 1, wherein the first signal includes a signaledge, and the control circuitry synchronizes the transmission timing ofthe second signal based on the signal edge of the first signal.
 3. Theactive stylus of claim 1, wherein the signal reception circuitryreceives the first signal in bursts, and the control circuitrysynchronizes the transmission timing of the second signal based on thebursts.
 4. The active stylus of claim 1, wherein the signal receptioncircuitry receives the first signal in bursts, respectively in timeintervals, and the control circuitry synchronizes the transmissiontiming of the second signal based on a gap between the time intervals.5. The active stylus of claim 1, wherein the first signal iscode-modulated with a first code, which is different from a second codeused to code-modulate the second signal.
 6. The active stylus of claim1, wherein the first signal includes configuration data, and the controlcircuitry configures the active stylus based on the configuration data.7. The active stylus of claim 1, wherein the first signal includes apower management command, and the control circuitry manages power basedon the power management command.
 8. The active stylus of claim 1,wherein the first signal includes a user feedback command, and thecontrol circuitry controls the active stylus based on the user feedbackcommand.
 9. The active stylus of claim 8, wherein the user feedbackcommand is a command that controls an LED provided on the active stylus.10. The active stylus of claim 1, wherein the first signal includes datathat defines one or more of a frequency, timing, and phase of the secondsignal to be transmitted from the active stylus, and the controlcircuitry controls the signal transmission circuitry based on said dataincluded in the first signal.
 11. The active stylus of claim 1, whereinthe signal reception circuitry receives the first signal in bursts,respectively in time intervals, and the signal transmission circuitrytransmits the second signal in a gap between the time intervals.
 12. Theactive stylus of claim 1, wherein the control circuitry controls thesignal transmission circuitry to transmit the second signal afterreception of the first signal by the reception circuitry ends.
 13. Theactive stylus of claim 1, wherein the control circuitry controls thesignal transmission circuitry to transmit the second signal at differentreporting rates under different conditions.
 14. A method of controllingoperation of an active stylus configured to provide input to a sensorarray including a matrix of electrodes, the method comprising: receivingfirst signal from the sensor array based on capacitive coupling betweenthe active stylus and the sensor array; transmitting, in response to thefirst signal, second signal to the sensor array based on capacitivecoupling between the active stylus and the sensor array; andsynchronizing transmission timing of the second signal to the sensorarray with reception timing of the first signal from the sensor array.15. The method of claim 14, wherein the first signal includes a signaledge, and the synchronizing step synchronizes the transmission timing ofthe second signal based on the signal edge of the first signal.
 16. Themethod of claim 14, wherein the receiving step receives the first signalin bursts, and the synchronizing step synchronizes the transmissiontiming of the second signal based on the bursts.
 17. The method of claim14, wherein the receiving step receives the first signal in bursts,respectively in time intervals, and the synchronizing step synchronizesthe transmission timing of the second signal based on a gap between thetime intervals.
 18. The method of claim 14, wherein the first signal iscode-modulated with a first code, which is different from a second codeused to code-modulate the second signal.
 19. The method of claim 14,wherein the first signal includes configuration data, and the methodfurther comprises: configuring the active stylus based on theconfiguration data.
 20. The method of claim 14, wherein the first signalincludes a power management command, and the method further comprises:managing power based on the power management command.
 21. The method ofclaim 14, wherein the first signal includes a user feedback command, andthe method further comprises: controlling the active stylus based on theuser feedback command.
 22. The method of claim 21, wherein the userfeedback command is a command that controls an LED provided on theactive stylus.
 23. The method of claim 14, wherein the first signalincludes data that defines one or more of a frequency, timing, and phaseof the second signal, and the method further comprises: controlling oneor more of the frequency, timing, and phase of the second signal basedon said data included in the first signal.
 24. The method of claim 14,wherein the receiving step receives the first signal in bursts,respectively in time intervals, and the transmitting step transmits thesecond signal in a gap between the time intervals.
 25. The method ofclaim 14, wherein the transmitting step transmits the second signalafter the receiving step of the first signal ends.
 26. The method ofclaim 14, wherein the transmitting step transmits the second signal atdifferent reporting rates under different conditions.